From ea637639591def87a54cea811cbac796980cb30d Mon Sep 17 00:00:00 2001 From: Jie Zhang Date: Mon, 14 Dec 2009 18:00:02 -0800 Subject: nommu: fix malloc performance by adding uninitialized flag The NOMMU code currently clears all anonymous mmapped memory. While this is what we want in the default case, all memory allocation from userspace under NOMMU has to go through this interface, including malloc() which is allowed to return uninitialized memory. This can easily be a significant performance penalty. So for constrained embedded systems were security is irrelevant, allow people to avoid clearing memory unnecessarily. This also alters the ELF-FDPIC binfmt such that it obtains uninitialised memory for the brk and stack region. Signed-off-by: Jie Zhang Signed-off-by: Robin Getz Signed-off-by: Mike Frysinger Signed-off-by: David Howells Acked-by: Paul Mundt Acked-by: Greg Ungerer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/nommu.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'mm/nommu.c') diff --git a/mm/nommu.c b/mm/nommu.c index 9876fa0c3ad3..8687973462bb 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1143,9 +1143,6 @@ static int do_mmap_private(struct vm_area_struct *vma, if (ret < rlen) memset(base + ret, 0, rlen - ret); - } else { - /* if it's an anonymous mapping, then just clear it */ - memset(base, 0, rlen); } return 0; @@ -1343,6 +1340,11 @@ unsigned long do_mmap_pgoff(struct file *file, goto error_just_free; add_nommu_region(region); + /* clear anonymous mappings that don't ask for uninitialized data */ + if (!vma->vm_file && !(flags & MAP_UNINITIALIZED)) + memset((void *)region->vm_start, 0, + region->vm_end - region->vm_start); + /* okay... we have a mapping; now we have to register it */ result = vma->vm_start; -- cgit v1.2.2